Closed-circuit classifier



June 9,1925. 1,541,237 R. S. TROTT CLOSED CIRCUIT CLASSIFIER Filed Dec.24. 1923 Patented June 9, 1925.l

nonmmpK s. Tno'r'r, or DENVER, comme.

CLOSED-cinema cLAs'snIEB..

Application led December T o all 'whomz't may concern:

Be it known that I, ROLLAND a citizen of the United States, residin Si.Tno'rr, at

Denver, in the'county pf Denver and tate 1 d `The launder 8, is pivotedat 9 and its 6 of Colorado, have invented certain new an usefulImprovements in Closed-Circuit Classifiers, of which the following is aspecification.

My invention consists of a closed circuit 10 classifier unit formed bythe combination 'of a sloping trough classifier with Va pulp thickener,and with certain other parts and novel details of construction. .A

The object of my invention Vis to provide a construction whereby thesaid sloping trough classifier and the said pulp thickener may beoperated in closed circuit withA each otherfor fthe purpose of theresulting beneits in operation and classification. A further object isto provide-al construction whereby a classifier and a thickener,operating as a unit in closed circuit with each other, may be set for acertain result and will thereafter be automatically regulated tomaintain thatresult.

In the drawings, Figure 1 shows a fragmentary vertical section of myclosed circuit classifier unit; and Figure 2 shows a plan view of thesame.v The support-of the upper end of the yshaft 22 is cut away, andithe bevel gear on the shaft 22 is indicated `by two dotted circles, forthe sake of clear-v ness.

The classifiertank 1, is provided withthe '35 extension 4, down alongits slope and which has a top or ture 6. Y A

` The rakes 2, are made of suiiicieht length to rake settled materialfrom the slope of 40 the extended tanky and they may be operat Y by anyproper power driven mechanism desired, so long as they rakethe settledmaterial Iup the slope of -the tank to the disvdeck 5, provided with theaperv charge lip 3. A; double rakeis shown, but a single rake may be^used if desired. The

rake operating 'mechanism shown is that covered yby my patent issuedSeptember 25th, 1923, .Number 1,468,844, but any other proper mechanismmay be-used in its-place if desired.

vThe tank 1, is also Aprovided with the adjustable overflow lip 7,though any other 24, 1923. serial ivo. cauo.

proper method' of controlling the height of the llquid level, W, of theclassifier 'by change of the height of the overflow lip,

may be employed, if desired.

other end is supported by' the hanger'lO,

adjustable in -length and hanging from an arm of the lever 11. The lever11 is supported. and pivoted at12 and carries the movable counterweight13, and the third arm 14.

The control rod 15, adjustable for length,

isl connectedto the arm 14 and to the lever 16 of the pulp valve 17.

I am well aware that various modiications of this launder` controlledvalve mechanism may be employed, but whatever mechanical equivalentisused, the essential point is that the mechanism should be such that itenables variation in the density in the -thickener to control the pulpfeed by means of the resultingwariation in the over- Iiow from theclassifier. And Ain, some classes of rwork the control of the pulp feedby the launder may be omitted and the launder made stationary, orintegral with the tank of the classifier or integral with thethickener,but in any case the result is the same in that lthe classifier and thethickener are operating in closed circuit with the resulting inherentautomatic regulation mentioned before.

I am also aware that 'the pulp valve 17 may be of any proper form ortype desired and may be used to by-pass the pulp feed back to a sump orin any other way as a means of controlling the amount that gets tothethickener. y 1

4But, whatever mechanical equivalent is ed' used, the result is thesame. in that the amount of pulp ted to the thickener is controlled bythe valve or other means operated by the launder as determined by theamount of overflow from the classifier.

The thickener tank 18'is provided with the feed box 28, the overiow lip19 and the discharge orifice 20 and is properly attached totheclassifier tank 1 so that the orifice 20 registers with the' aperture 6of the deck 5 of the tank extension 4, forming apassage 26, between thethickener and thev classifier.

Any other proper method of attaching the thickener to the classifier maybe employed so long as it allows the thickener to discharge settledmaterial into the classifier below its liquid lever, W, so that byallowing the overflow from the classifier to go to the thickener the twomachines will operate in closed circuit.

The sweeps 21, attached to the shaft 22, are supported and slowlyrevolved by the belt pulley and gearing as shown, or by any other properpower mechanisnnlso that the settled material will be moved to thedischargeorifice 2O and the passage26.

The sleeve 25 may be secured upon the portion of the shaft 22 whichextendscbelow the Sweeps 21, if it is desired to reduce the active crosssectional area of the passage 26., By variation of the outside diameterof the sleeve 25 any desired reduction of the passage 26 may beobtained.

,I am well aware that there are various other ways to adjust or controlthe active area of the passage 26, butin any .case the result is thesame in that the ability to vary the area of the passage 26 will assistin obtaining the proper relations between the amount of pulp fed to thethickener, the density -in the thickener` the height of the overflow lipof the classifier, and the amount of wash water or other liquid fed' tothe classifier.

Wash water, or other liquid is fed to the classifier from the trough 23which is fed from the valve controlled feed pipe 24, or

' it may be supplied "in any other; proper way` and from any otherproper source. I

f The tank l is provided with a drain 27 of any proper construction sothat the tank 1 may be drained or washed out.

Thev product discharged by the rakesi2 may be taken away by a conduit,launder, pipe, conveyor, trough or any other proper means.

The overflow from the classifier may be taken away by a conduit,launder, pipe, trough or any other proper means. y

Pulp is fed to the thickener and wash water or other liquid is fed tothe classifier in such quantity that there is always an overflow at theoverflow lip of the classifier, which overow mixes with the feed to thethickener either in the thickener itself or'- before the feed gets tothe thickener.

'As the level of the overflow lip and of the liquid in the classifier ishigher than the overflow lip and the liquid inthe thickener, there willbe an upward current through the aforesaid adjustable passage from theclassilier to the thickener.y

The settled material from the thickener will have to pass down into theclassifier against the upward current through said passage, the lightersolidsvand suspensions overowing from the overflow lip 0f the thickener.v

moved by the rakes beyond the influence ofl the said current.

These re-suspended solids and suspensions beyond the influence of thecurrent from the classifier to the thickener, will either settle and beraked out of the classifier, or they will overflow from the overflow lipof the classifier into the launder and flow on into the thickener, fromthe launder.

rIhe classifier end of the launder is pivotally mounted; the thickenerend of the launder being suspended from a pivotedand counterweightedlever which is connected to a valve controlling the pulp feed to thethickener.

The entire launder may be hung from this lever if desired, and a springinstead of the counterweight may be employed to sustain one or both ends0f the launder in any proper way, though l p-refer'to use theconstruction as stated.

But, regardless of the mechanical equivalent employed, the movementofthe launder,

due to the variation of the amount of overflow and of the weight) itcarries, operates controls which vary the amount of pulp fed to thethickener., i

rlhus` when the amount of pulp fed to the thickener increases, thedensity in the thickener increases and the upward current in the passagebetween the classifier and the thickener will decrease.

So, the overflow from the classifier, due to wash water or other liquidwill increase.

This will increase the weight in the launder and it will be depressed,which movement will operate the controls and reduce the amount of pulpfed to the thickener.

"lhe reduced feed to the thickener, coupled with the increased amount ofoverflow from A the classifier. which flows into the thickener, willreduce the density in the thickener'.

This reduction in density will increase the upward flow between theclassifier and the thickener, which in turn Awill decrease the amount ofoverow and the weight carried by the launder.

This will cause the launder to rise, which movement will operate thecontrols to open the feed pulp valve and increase the feed to thethickener.

ln other words, by the proper setting of the launder support and of thecontrols which govern the pulp feed, together with the proper setting ofthe active area of the passage `from the classier to the thickener,

lll@

the height of the classifier overflow lip, and of the amount of washwater or other liquid fed to the classifier, the machine may be set tooperate at maximum efficiency for any material being fed and for anydesired classification; and the operation of the classifier overfiow inclosed circuit with the thickener, controlling by the action of thelaunder the amount of pulp fed, will maintain the machine automaticallyat this point of greatest efciency.

In some cases it may be found necessary to cut down the effectivesettling area of the thickener by shortening the power driven sweeps,but this is a step ywell understood by those versed in thickener's. v

In other classifiers of this type, when the lighter solids andsuspensions have been carried beyond the influence of the current fromthe classifier to the thickener there is no chance for them to get outof the classifier except by settling and being raked out with theheavier settled material.

In my invention, however, since the olassifier is in closed circuit withthe thickener, these suspensions and lighter solids may overflow andpass back to the thickener eventually or directly, where they haveanother opportunity to overflow from the overflow lip of the thickener.

It will be seen that this will give a product delivered by the rakes ofthe classifier which is much cleaner than has hitherto been possible, asit will be much more free from the Vlighter solids and suspensions.

In some cases it will be found" that the classifier and the thickenerbeing in closed circuit will furnish enough automatic regulation withoutthe necessity of controlling the feed to the thickener by the action ofthe launder.

'Ihat is, increase of the density in the thickener will cause moreoverflow from the classifier, which will tend to thin down the contentsof the thickener and thus lower its density and reduce the classifieroverflow. But in any case, it will probably be found that the laundercontrol of the pulp feed at the start of any new set of conditions willassist in the determination of the passage area, of the pulp feed, ofthe height of the classifier overflow lip, and of the amount of yvashwater or other 4liquid fed to the classi- And should either thecharacter or the quantity of the pulp to the thickener change for anyreason, or a'difl'erent classification be desired, the overflow launderpulp control will assist the operator in quickly arriving atthe newsettings for maximum efii.

ciency of the machine.

When proper settings are obtained it may be possible that the laundermay be blocked in position or in any other proper way'may be madestationary, and the regulation due employed.

The operation of my closed circuit classifier is as follows ;-Pulp is,fed to the thickener and wash water or other liquid is fed to theclassifier in the desired quantities, the overfiow from the classifiergoing to the thickener direct as shown, or it may, if desired, go to thepulp feed before it reaches the thickener.

As the density of the fmaterial in the thickener is greater than that ofthe material in the classifier, the overflow lip of the classifier willhave to be adjusted to a slightly higher level than the overflow lip ofthe thickener in order to produce'the desired upward current through theconnect. ing passage from the classifier to the thickener.

The settled material from the thickener will have to pass downwardagainst this upward current, which carries the lighter solids andsuspensions up to either re-settle in the thickener, or to overflow atits overfiow lip.

I have now described my closed circuit classifier unit in the form Iprefer, but I do not wish to be limited to the exact constructionsdescribed, as I am well aware of various modifications that may be madewithout ydeparting from the essence of my invention, which is; thecombination of the thickenerl and the classifier with other parts andnovel features of construction to the end that they may form a closedcircuit classifier unit capable of adjustment for superiorclassification and practically automatic regulation of suchclassification.

So, what I claim as new, and desire to protect by Letters Patent is asfollows z- 1. A' classifier unit, comprising in combination, a.thickener and a classifier, each provided with an overflow, theclassifier having an outlet above its liquid level, a device for movingsettled material to said outlet and an'aperture below its liquid level,the thickener having a bottom surface adapted to receive settlingmaterial, and being provided with a discharge orifice and with a ldevicefor moving settled material toward flow, the classifier having an outletabove its liquid level and a device for moving settled material to saidoutlet, the thickener having a bottom surface adapted to receivesettling material and being provided with a discharge orificeand 'adevice for moving settled material toward said orifice and meansadjacent said orifice joining said thickener to said classifier belowthe liquid level of the classifier, means for feeding material to thethickener, means for feeding a liquid to the classifier, and means forconveying the overflow from the classifier to the thickener. L

3. A classifier unit comprising a thickener and a classifier in closedcircuit, each provided with an overflow, the thickener being providedwith a discharge for thickened material and with means connecting saiddischarge to the classifier below its liquid level, and vwith means toconvey settled material to said discharge, the classifier being providedwith an outlet above. its liquid level and with means to convey itsoverflow to said thickener, the thickener being provided with means forfeeding material and the classifier being provided with means to feed aliquid.

4:. A classifier unit comprising in combination a thickener and aclassifier in closed circuit, each provided with an overflow and adischarge, the thickener discharge being into the classifier below itsliquid level, the classifier discharge being above its liquid level,each being provided with a device to move settled material toward itsrespective discharge, the classifier being adapted to overflow into thethickener, and being provided with a source of wash liquid, thethickener being provided with a source of feed pulp.

5. A classifier unit comprising in combination a thickener provided withan overflow and a discharge and a device to move settled material towardsaid discharge, a classifier provided with an overflow, with `a feedhole below the liquid level, with a discharge above the liquid level,and with a device to move settled material to said discharge, theclassifier adapted to overflow into the thickener, and the thickeneradapted to discharge into the classifier through the said feed hole,means for feeding material to the thickener, and means for feeding washliquid to the classifier.

6. A classifier unit comprising in combination a thickener provided withan overflow and a discharge and a device to move settled material towardsaid discharge, a classifier provided with an overflow, with a feed holebelow the liquid level, with a discharge above the liquid level, andwith a device to move settled material to said discharge, the thickeneradapted to ,discharge into the classifier through the said feed hole,means for feeding a liquid to the classifier, means for feeding materialto the thickener, means to vary the amount of material fed to thethickener, a launder adapted to carry the overflow from the classifierto the thickener, and adjustable means connecting said launder to Saidlast named means to vary the feed to the thickener in inverse proportionto the amount of overflow carried by the launder.

7. A classifier unit comprising in combination a thickener and aclassifier, each provided with an overflow, and with a discharge forsettled material and with a device for moving settled material to saiddischarge, the thickener discharge being below its overflow level anddischarging material from the thickener into the classifier, and theclassifier discharge being above its overflow level, a launderforconveying the classifier overflow to the thickener, and adjustable meansoperated by said launder to control the amount of material fed to thethickener inversely to the amo-unt of overflow carried by the launder.

8. A classifier unit comprising in combination a thickener and aclassifier, each provided with an overflow, and with a discharge forsettled material and with a device for moving settled material to saiddischarge, the thickener discharge being below the overflow levels ofboth thickener and classifier and discharging material from thethickener into the classifier, and the classifier discharge being aboveits overflow level, means to feed material to the thickener, a launderto convey the classifier overflow to the thickener, a control governingthe amount of material fed to the thickener, and adjustable meansconnecting said control and said launder such that an increase ofoverflow carried by the launder will act to operate the said control anddecrease the feed to the thickener, and a decrease of said overflow willincrease the feed to the thickener.

9. A classier u nit comprising in combination a classifier or secondarysettling chamber provided with a liquid overflow and means to adjust theheight thereof, and a thickener or primary settling chamber providedwith an overflow and adapted to receive the overflow from the secondarychamber, the secondary chamber having an outlet above the level of itsoverflow, and the primary chamber having a bottom surface adapted tocause the congregation of settling matter to a semi-solid condition, andin connection with said surface means joining the primary chamber to thesecondary chamber and forming a passage between them be- .neath theliquid level of the secondary chamber, a device for moving materialsettling upon the bottom of the primary chamber toward said passage,means for feeding material into the primary chamber, and a device formoving material settling in the secondary chamber along a slopingsurfacetor said outlet. l

10. A classifier unit) comprising in combination a thickener providedwith an overiowand with a discharge and with a dei .vice to move settledmaterial toward Said discharge, a classifier provided with an overflowadjustable in height, a feed hole below the level of said overflow, adischarge above Y 'the level ofv said overflow, and a device to movesettled material to said discharge, the thickener adapted to dischargeinto the classiiier through said feed hole, means for feeding materialto the thickener, control means to govern the amount of material fed tothe classifier, and means conveyin theoveriow from the classifier to thethic ener and adjustably connectedl to said control means to vary thefeed tothe thickener inversely with the amount of said overflow.

11. A classifier `unit comprising in combination a classifier orsecondary chamber provided with a liquid overow adjustable n hei-ght,and a'thickener or primary settling chamber provided with an overflow,the secondary chamber having an outlet-above the level of its adjustableoverflow, and the pri-l mary chamber having va bottom surface adapted tocause the congregation of settling matter to a semi-solid condition, andin connection with said surface means joining the primary chamber to thesecondary chamber and forming a passage between ythem beneath the saidoverflow ofthe secondary chamber, a device for moving material settlingupon the bottom of the primary chamber toward said passage, a device formoving material settling in the secondary chamber along a slopingsurface to said outlet means for feeding material into the prifeed hole,liquid to the classifier,

.mary

'chargea classifier provided with an overfiow, with afeed hole below theliquid-level, a discharge above the liquid level, and with a device tomove settled material to said discharge, .the thickener adapted todischarge into the classifier through the said means for feeding wateror other means for feeding material t/the thickener, means to vary theamount of material fed to the thickener, a launder adapted to carrytheoverow from ried bythe launder.

the classifier to the thickener, and means connecting said launder tosaid last named means to` vary the feed to the'thickener by he variationof the amount of overflow car- 13. A classifier unit comprising incombination, a thickener and a classifier, each provided with anoveriow, and with a discharge for settled materialJ and with a devicefor moving settled material to said discharge, the thickener dischargebeing below its liquid level and discharging material from the thickenerinto the classifier, andthe classifier discharge being above its liquidlevel, means for mixing the classifier overflow with the thickener feed,and means operated `by said firsty means to control the amountof'material fed to the thickener by the variation of the amount ofoverflow car.

ried by said first means.

14. In a classifier, primary and secondary settling chambers, having anoverflow for suspended fines, rand at a lower point, having arestrictedo en ing for the passage of material to and rom the secondary chamber,and the secondary chamber having an outlet for the coarse V"product,meansv for feeding pulp into the primary chamber, a mechanical devicefor dragging settled material alonga sloping surface to the outlet ofthe secondary chamber, means for feeding a liquid to the secondarychamber, the secondary chamber having an overflow for suspended fines,

the feed to the thickener.

15. In a classier, primary and secondary settling chambers, each chamber`having an overow for the suspendedfines, the Aprimary chamber having ata point lower than its overflow, a restricted opening for the passage ofmaterial to and from the sec-` ondary chamber, and the secondary chamberhaving an outlet for the coarse product, meansj for feeding pulp intothe primary chamber, means for feedingar, liquid to the secondarychamber, means mixing the overiiow and

means conveying s aid overflow to mixvlwith ,1.00

from the classifier with the feed to the the primary chamber thickenerand means to control the amountv l of said feed by the variation in theamount of said overflow, and a mechanical device for dragging materialalong asloping surface 'to the outlet of the secondary chamber. 16. In aclassiiier, primary and secondary chambers, the, primary chamber havinganA overiiow for the suspended fines and, at a lower point, having arestricted opening for the passage of materia-l to vand from thesecondary chamber, and the secondary chamber having an outlet for thecoarse product,

means for feeding pulp into the primary y chamber, a mechanical devicefor dragging settled material along a sloping surface to the' outlet ofthe secondary chamber, ymeans for feeding a liquid to the secondarychamber, a mechanical device to impel settled matter along the bottom ofthe primary chamber to the opening thereof, the second-v ary chamberhaving an overflow for the suspended fines, and means conveyinfg theclassilier overflow to mix with the eed to the thickener.

17. In a classifier, primary and secondary settling chambers, eac'hchamber havmg an overflow for the suspended fines, the primary chamberhaving at a point lower than its overflow, a restricted opening for thepassage of material to and from the secondary chamber, and the secondarychamber having an outlet for the coarse product, means for feeding pulpinto the primary chamber, means for feeding a liquid to the secondarychamber, means for mixing the overflow from the classier with the feedto the thickener and means to control the -amount of said feed by thevariation in the amount of said overflow, a mechanical device fordragging settled material along a sloping surface to the outlet of thesecondary chamber, and a mechanical device to impel matter along thebottom of the primary chamber to the o ening thereof.

18. In a classi er, primary and secondary settling chambers, thesecondary chamber having an overflow and an outlet for the coarseproduct, and the primary chamber i ary chamber with having an overflowand comprising a shallow vessel with `a substantially level bottom,provided with an opening for the flow of material to and from the`secondary chamber, means for feeding pulp into the'primary chamber, amechanical device to impel settled matter to the opening of the primarychamber, a mechanical device for dragging settled material alonga/sloping surface to.

chamber, and

the outlet of the secondar means to mix the overflow rom the seconda thefeed to the primary chamber.

19. ln a classifier, primary and secondary settling chambers, thesecondary chamber having an overflow, and an outlet for the coarseproduct, and the primary chamber having an overflow and comprising ashallow vessel with a substantially levelbottom provided with an openingfor the flow of material to and from the secondary chamber, means forfeeding pulp into the primary chamber, a mechanical device to impelsettled material along a sloping surface to the outlet of the secondarychamber, and means to mix the overflow from the secondary chamber withthe feed to the primary chamber and means to control the amount of saidfeed by the variation in the amount of said overflow.

20. Thel combination with afclassiier including a trough having anoverflow and a sloping bottom, an outlet at .the u per end thereof, anda reciprocating rake o1 dragging material along said bottom to saidoutlet, of a settling chamber disposed above the lower portion of saidsloping bottom and having an overflow for liquid and suspensions, and ata lower point having an opening for the passage of material to and fromsaid trough, means for feeding pulp into said settling chamber, meansfor the supply of a liquid to the trough, and means to mix the overflowfrom the trough with the feed to the settling chamber.

21. The combination with a classifier in-` pulp into said settlingchambers, means for v the supply of a liquid to the trough, a mechanicaldevice to impel settled matter along outlet,"

Cil

the bottom of said settling chamber, to the opening thereof, and meansto convey the overllowfrom the trough to mix with the feed to thesettling chamber.

22. The combination with a classifier in cluding a'trough having anoverflow and means to adjust the height thereof, a sloping bottom, anoutlet at the upper end thereof, and a reciprocating rake for draggingmaterial along said bottom to said outlet, of a settling chamberdisposed above the loc lower portion of lsaid trough and having an voverflow for liquid and suspensions, and in its bottom having an openingfor the passage of material toand from the trough', means for feedingpulp into said settling chamber, means for the supply of a liquid to thetrough, a mechanical `device to impel settled matter along the bottom ofsaid settling chamber to the opening thereof,

and means to convey the overflow from saidtrough.

23. In a classifier, primary and secondary settling chambers, theprimary chamber having an overflow for suspended fines, and at a lowerpoint having an opening for the passage of material to and from thesecondary c iamber, and the secondary chamber having an overflow for liuid yand) suspensions and means to adjust t 1e heivht thereof and anoutlet for the coarse procuct., means for feeding pnl i to the primarychamber and means for t 1e supply of a liquid to the secondary chamber.

2l. In a classifier, primary and secondary settling chambers, theprimary cham-k ber having an overflow for suspended fines, and at alower point having an opening for the passage. of material to and fromthe secondary chamber. and the secondary chamber having an overflow forliquid and suspensions and an outlet for the coarse product, means for`feeding pulp to the primary chamber, means for the supply of a liquid tothe secondary chamber, and

means to convey the overflow from the sec 1 sions and means to adjustthe height thereof and an outletl for the coarse product, means forfeeding pulp into the primary chamber, a mechanical device for draggingsettled matter along a sloping surface to the outlet of the secondarychamber, and

a mechanical device to v.impel-settled matter alonv the bottom of theprimary chamber to the opening thereof;

26. In a classifier, Aprimary and secondary settling chambers, theprimary chamber having an overflow for suspended fines, and in itsbottom having an opening for the passage of material to and from thesecondary chamber, and the secondary chamber having an overflow forliquid and suspensions and means to adjust the height thereof and anoutlet for the coarse product, means for feeding pulp into the primarychamber, a mechanical device for dragging settled matter along a slopingsurface to the outlet of the secondary. chamber,

a mechanical device to impel settled matter along the bottom of theprimarychamber to the opening thereofLand means to convey the overflowfrom the secondary chamer. E s

27. In a classifier, primary and secondary settling chambers, theprimary chamber havmg anpverflow for suspended fines andk in its bottomhaving an opening for the .passage of material to and from the secondarychamber, and the secondary chamber hav- Y ing an overflow for liquid and`suspensions and an outlet for the coarse product, means for feedingpulp into the primary chamber,

a mechanical device for dragging settled mat'- ter along a slopingsurface to the outlet of the secondary chamber, a mechanical device toimpel settled matter along the bottom of the primary chamber to the`opening there-v of, and means to convey the overflow from `the secondarychamber and to vary the amount of feed to the primary chamber by thevariation in the amount of lsaid .over-l flow.

28. In a' classifier, primary and secondary settling chambers, eachchamber having an overflow for the suspended ines, the

the secondary chamber and to control the.

amount of feed to the primary chamber by the variation in the amount ofsaid overflow,

.a mechanical device for dragging settled material along a slopingsurface to the outlet of the secondary chamber, .and a mechanical deviceto impel matter along the bottom of the primary chamber to the openingthereof.

29. In a classifier, primary and secondary settling chambers, thesecondary chamber having an overflow and means to adjust the heightthereof, and an outlet for the coarse product, and the primary chambercomprising a shallow vessel with a substantially level bottom, having anopening for the flow of material to and from the secondary chamber,means for feeding pulp into the primary chamber, a mechanical device toimpel settled material along a slopingjsurface to the outlet of thesecondary chamber, and means to convey the overiiow from the secondarychamber. A

Y 30. In a classifier, primary andsecondary settling chambers, thesecondary chamber having an overiow, and an outlet for the coarseproduct, and the primary chamber comprislng a shallow vessel with asubstantially level bottom, and with an opening for the iow of materialto and from the secondary chamber, means for feeding pulp into theprimary chamber, a vmechanical device to impel settled matter to theopening of the primary chamber, a mechanical device for dragging settledmaterial along a. sloping surface to the outlet of the secondarychamber, and means to convey the overflow from the secondary chamber,and means to control the amount of feed to the primaryhaving an overl owfor liquid and suspen- .sions and at a lower p oint having an o nl. Vingfbr the passage of material to andm said trough-means for feeding pulpinto said settling chamber, means forthe supply of aliquid to thetrough, andmeans to convey-the overflow from said trough.

32. A classifier unit comprismg'in comprimary chamber having ata pointlowcrbinationaI thickenerprovided with an overy flow and a discharge anda device to movel fcharge, the thickener adapted to discharge into theclassifier' through the said feedfhole,

' means for feeding a liquid to the classifier,

means for feeding material to the thickener, means to vary the amount ofmaterial fed to the thickener, a launder adapted to carry the overfiowfrom the classifier, and means connecting said launder to said lastnamed means to vary the feed to the thickener by the variation of theamount of overflow carried bythe launder. e

33. A classifier unit comprising in combination a thickener and aclassifier, each provided with an overfioW and with a. discharge forsettled material and with a device for moving settled material to saiddischarge, the thickener discharge being below its liquid level and'discharging material from the thickener into the classifier, and theclassifier discharge being above its liquid level, means conveying theclassifier overflow from the classifier, and means operated by saidfirst means to control the amount of material fed to the thickener-bythe-variation of the amount of overflow carried by said first means.

34. In a classifier, primary and secondary settling chambers, theprimary chamber havmams? ing au overfiow for the suspended fines, and ata lower point having an opening for the passage of material .to and fromthe secondary chamber, and the secondary chamber having an outlet forthe coarse product, means for `feeding pulp into the primary chamber, amechanical devicev for dragging settled material along a sloping surfaceto the outlet of the secondary chamber, means for feeding a liquid tothe secondary chamber, the secondary chamber having an overfioiv forsuspended fines and means t0 adjust the height thereof.

35. In a classifier, primary and secondary settling chambers,eachchamber having an overfiow for the suspended fines, the primarychamber having at a lowerlpoint than its overfiow an opening for thepassage of material to and from the secondary,and the secondary chamberhavingan outlet for the coarse product, means'for feeding pulp into theprimary chamber, means for feeding a liquid to the secondary chamber-,E*means to convey the secondary chamber overflow from the secondarychamber, means to control the amount of said pulp fed to the primarychamber by the variation in the amount of said overfiow, and amechanical device for dragging settled material along a sloping surfaceto the outlet of the secondary chamber, v

In testimony whereof I affix my signature.

ROLLAND s. TROTT.

